Microhabitats of stream invertebrates on two submersed macrophytes with contrasting leaf morphology

Larvae of Chironomidae, Simuliidae and Trichoptera exhibited various patterns of micro‐distribution on the submersed macrophytes Potamogeton×zizii, with broad leaves, and P. pectinatus, with thread‐like leaves. Seven common species of chironomid, six belonging to the subfamily Orthocladiinae and one to the Chironominae, showed four distinguishable patterns of distribution. The density of Simulium larvae was much greater towards the apices of the stems on both plants. Among three species of Trichoptera studied, the predatory Rhyacophila dorsalis had a pattern of distribution which was strongly related to prey density, particularly that of Simulium, on P. ×zizii, but not on P. pectinatus. P. ×zizii supported proportionately more free‐ranging scrapers, such as the chironomid Thienemanniella vittata. than did P. pectinatus while the reverse was true for filter‐feeders. These patterns are discussed in relation to habitat structure and behavioural characteristics.